Understanding Weight
Understanding proper weight distribution, and the impact weight can have on the relationship between car and caravan is critical to optimising towing stability and ensuring the safety of you, your family, and other road users.
Being under all your weight compliances and road worthy is one thing. Being set up for optimal towing stability is another all together. It is possible to be weight compliant but not necessarily stable at the same time.
Have you ever looked at a car and caravan driving down the road and thought to yourself that doesn't look very balanced? It could be because the tow ball ride height is not appropriately set. Think about this: two friends by exactly the same caravan. One drives a 300 series landcruiser with a standard tow ball ride height of around 750mm from the ground. The second friend has a Sangyong Rexton with a tow ball ride height of around 450mm. It is highly unlikely that both caravans in this scenario will tow the same behind these two very different vehicles. It is fair to assume one or both friends will need to adjust their tow ball ride height to allow their respective caravans to tow at their best. Having the tow vehicle and caravan level is a great place to start but does not always guarantee the optimal towing performance, stability and safety.
We measure against the following weight distribution benchmarks in our weight studies.
TBD
We look for between 7 -12% of the total weight of the caravan (ATM) resting on the tow ball, with the sweet spot around 10%. Too little is as bad as too much tow ball download (TBD). Remember the one point of contact that gives you control of the caravan is the tow ball. If the tow ball and coupling are firmly connected you have good control. If not you can lose control very easily. There are a few exceptions to the rule, like light weight European caravans that are designed to be towed by smaller vehicles that have reduced tow ball download capacities.
Caravan Axle Weight Balance
We are also concerned about weight distribution between the axles on a tandem axle caravan. It is not uncommon to see caravan setups where you have one axle carrying far more weight than its partner. This does not make for stable towing when one axle is overloaded and the other having a bit of a holiday. Particularly if it is the rear axle that is overloaded. Ideally we need slightly more weight on the front axle but no more than 10% more or between 80 -100kg.
Front to Rear Axle Weight Transfer - Tow Vehicle
We will look for something less than a 7% weight transfer from the front axle of the tow vehicle to the rear axle. As a general rule of thumb for every kg placed on the tow ball of the vehicle, leverage will move 500g from the front axle and place it on the rear axle. (A 300kg TBD will move something around150kg off the front axle). 7% - 10% is an area of concern and greater than 10% is a must fix scenario. A gross vehicle mass (GVM) upgrade will help to some degree. The installation of rear airbags will help maybe 10kg at best. The most practical answer is the introduction and use of a weight distribution hitch. A properly adjusted WDH will rotate the 150kg straight back onto the front axle of the vehicle. As far as the use of a WDH, you either need one or you don't.
Tow Ball Ride Height
Tow ball ride height (TBDH) can have a profound influence on all of the above A) TBD B) caravan axle weight balance and D) front to rear axle weight transfer - tow vehicle. The optimal TBRH you require for a touring caravan will be different to a full off road caravan. As a general rule 1 mm change in TBRH can equate to 1kg. (A 50mm change will usually equal a 50kg change in TBD.
This is why it is important to weigh your car and caravan together at least once to ensure you are set up for success....